Re: XML::LibXML - Mixing XPath with a document fragment

On čt 29. ledna 2009, Emmanuel Rodriguez wrote:
> Hi,
>
> I have an XML document that was generated with document fragments
> by an external function. This gave me some struggle because I was
> trying to use an XPath expression to access some nodes and
> couldn't reach them. This is due to the fact that even though the
> document fragment seems transparent it's still in the document
> and brakes the parent/child/sibling relation ship. This makes it
> a difficult to use XPath to search for nodes.
>
> Is there a way to clean document of all document fragments
> besides $xml =
> XML::LibXML->new()->parse_string($xml->toString()); ? Should
> document fragments be avoided?
>
> For the curious, I have attached a test case that shows the
> problems I had parsing the document.

Hallo Emmanuel!

A fragment node should never have appeared as a child of another 
node; that's the bug!

XML::LibXML should follow DOM spec [1], which says that attaching a 
document fragment to a node should result in moving the document 
fragment's children to the child list of the node, not in attaching 
the document fragment itself to the node. This seems to be a gap in 
XML::LibXML code, where addChild simply calls xmlAddChild without 
checking the node type; since xmlAddChild does not seem to do the 
job, I should add some code to handle fragments in a special way. 
addSibling seems to suffer from the same problem.

So the following part from your test case:

	# Add the child elements through a document fragment
	my $fragment = $xml->createDocumentFragment();
	$root->addChild($fragment);
	foreach my $id (1 .. 3) {
		my $node = XML::LibXML::Element->new('child');
		$node->setAttribute(id => $id);
		$fragment->addChild($node);
	}
	
should behave like a no-op, unless you rewrite it as

	# Add the child elements through a document fragment
	my $fragment = $xml->createDocumentFragment();
	foreach my $id (1 .. 3) {
		my $node = XML::LibXML::Element->new('child');
		$node->setAttribute(id => $id);
		$fragment->addChild($node);
	}
	$root->addChild($fragment);

in which case all nodes created inside the foreach loop and attached 
to the fragment should be re-attached to $root on 
$root->addChild($fragment), leaving the fragment empty.

I suggest you avoid calling addChild with a fragment as argument 
until XML::LibXML is fixed, which I'm gonna do now:-)

Thanks for pointing this out. Best,

[1] http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-B63ED1A3

-- Petr
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